Heat transfer



Reimed Aug. 7, 1934 UNITED STATES HEAT TRANSFER Thomas Midgley, Jr., Worthington, Albert L.

Henne, Columbus, and Robert R. McNary, Dayton, Ohio, assignors, by mesne assignments. to

General Motors Corpo Delaware ration, a corporation ol original No. 1,833,841, mea November 24. 1931. Serial No. 426,974, February 8, 1930. Application for reissue May 2s, 1934. sei-m No.

24 claim. (o1. eef-17s) This application relates to the art of transferring heat from one point to another and specifically to the art of refrigeration.

Heretofore, as far as we are aware, refrigerants 6 and heat transfer agents have been chosen chiefly for their boiling points and stability inthe refrigerating or heat transfer cycle irrespective of other desirable properties, such as non-inammability and non-toxicity.

It is the object of our invention, on the other hand, to provide a process of refrigeration and, generically, a process of heat transfer in which these desirable properties, such as non-inflammability and non-toxicity, are obtained in combination with the desired boiling points.

Broadly stated, the part` of our process which deals with the controlling of the properties of the refrigerating or heat transfer agents consists inL replacing hydrogen by iluorne or other halogen,

or both, in aliphatic hydrocarbons in which at least one hydrogen has already been replaced by fluorine.

Broadly stated, the part of our process which` relates to the transfer of heat or the production of refrigeration comprises changing the physical state of, for example, by condensing or evaporating, a halo-fluoro derivative of an aliphatic hydrocarbon, and dissipating to, or withdrawing from, an object to be heated or cooled, the latent heat necessary for changing the physical state of the said derivative. By a halo-nuoro deriva- `tive of an aliphatic hydrocarbon we mean a derivative containing more than one uorine atom with or without other halogen atoms, or one uorine atom with one or more other halogen atoms.

Referring nowspecically to our mode of controlling the properties of the refrigerating or heat transfer agent, aliphatic monouorides form the 40 .structural nucleus on which the agents are built. Broadly speaking, if in the structural formula CHaF we increase the uorine content (number of atoms) by the substitution of iiuorine for hydrogen, stability increases, inflammability decreases, and toxicity decreases. If we keep the fiuorine content constant and substitute another halogen for hydrogen in the nucleus, the boiling point increases, the stability decreases, the toxicity increases, and the 'inflammability decreases.

The degreeto which these variations take place depends on what the other halogenl (chlorine, bromine, or iodine) is. As'the ratio of the halogen content-to the hydrogen contentincreases the inflammability decreases.

Becausethere are several variables, and because of the value of relative proportions, we haveplaced the compounds of the group discussed on plots wherein Fig. 1 is a plot applying the rules of substitution to typical groups having one carbon atom,

Fig. 2 is a plot applying the rules to groups having two carbon atoms, and

Fig. 3 is a key to Fig. 2, showing the radicals corresponding to the numbers usedin Fig. 2.

Referring to the plots generally, Lthe dashedl lines indicate iiuorine substitutions and the solid lines indicate chlorine substitutions. Similar 'plots are obtained with bromine and iodine in place of chlorine except that the plot is elongated in the direction of higher temperatures with bromine,` while with iodine the temperatures are still more elevated. The amount of elongation is readily determined by applying the boiling points of some of these compounds.

Referring specifically to Fig. l, this plot contains all the compounds which can be derived from CHzF by chlorine and/or uorine substitutions, together with data which assist in the' formation of the plot.l On the base line appear the numerals zero tofourwhich show halogen content, and the vertical line gives the approximate boiling points in degrees centigrade. At each point of intersection is given the chlorine and uorine content andthe complete formula ofthe corresponding compound is found by making this halogen substitution for hydrogen -in the formula CH4. We-have drawn a horizontal dashed line at about 25 centigrade to indicate approximately the optimum vapor pressure conditions which we desire for operating an air cooled refrigerator'. It is obvious that one may deviate more or less from this line to obtain optimum conditions which include some other factors, so` that within the neighborhood of this line we can provide a suitablelrefrigerantto meet a wide variation in limitations imposed. If under other refrigerating conditions another optimum line is found desirable, the same choice may be made in Athe neighborhood of that line. In fact, the actual operation of the refrigerator and the providing of the characteristics of the refrigerant are here combined as one problem so as to obtain the most desirable process of refrigerationI under a given set of conditions.

In Figure 2 we have shown the same mode of controlling the properties of a refrigerant carried to compounds of the same -type as in Figure 1 but having two carbon atoms. The key to the chart is given in Fig. 3. For example compound 0.1 is CH:.CH2.F, compound 2.9 is CHFzCClzF, com- 110 CHJ-CH3F, which has a boiling point at about 32 C. If we make a fluorinesubstitution for hydrogen in the second radical of this structural f formula so that it reads CH3- CHR we have a other aliphatic mono-fluorides.

refrlgerating agent whose 'boiling point is about 26 C. If we make the iluorine substitution for hydrogen onto the other carbon atom so that the formula reads CHsF- CHzF the boiling point of this refrigerant is about 5 C. Thus, the nrst type of substitution yields a compound boiling substantially lower than the compound obtained by the second type of substitution', and the chart shows this to be general. -The substitution of chlorine, bromine,- or iodine for hydrogen raises the boiling point, but the substitution in a radical which does not already contain a halogen raises the boiling point more than when the substitution is made in a radical which already contains a halogen.

The plot may be expanded in like manner with As the number of carbon atoms increases the complexity and extent of the plot will increase together withthe number of halogens present. These halogen derivatives of aliphatic mono-nuorides may be represented by the formula CnHmFpXi in which C represents carbon and n the number of carbon atoms in the molecule which is always equal to one or more.

H represents hydrogen and m the number of atoms thereof, which may equal zero and still fulfill the requirements of our invention. Y

F represents iluorine and p the number of atoms thereof which is always equal kto one or -more.

X represents chlorine, bromine or iodine or combinations thereof and r the total number ofsuch atoms. r may be zero when p is greater l than one.

Among the chemical groups that these refrigerants fall in are halogen derivatives of aliphatic mono fluorides, halogen derivatives of alkyl mono iluorides, aliphatic iiuoro halides, alkyl uro halides, fluoro derivatives of methyl fluoride, fiuoro halo derivatives of methane and fluoro chloro derivatives of methane.

Thus by our mode of making iiuorine and/or other halogene substitution in a mono-iluoride, we can meet any conditions of refrigeration and provide our refrigerant with the desired properties, such as non-toxicity and non-infiammability, along with such properties as stability and proper boiling points.

Referring more speciiicaly to the part of our process which relates to the actual transfer of heat, we accomplish this transfer oi' heat by changing the physical state, of the refrigerant, for example, by condensing or evaporating our aliphatic hydrocarbon derivative which contains more than one uorine atom with or without other halogen atoms, or one fluorine atom with one or more-other halogen atoms, and by dissipating to or withdrawing from an object to be heated or cooled, the heat necessary for the change in physical state. More specically, to produce refrigeration, we may evaporate the desired derivative in the vicinity of a body to be cooled. while if a heating effect is desired, we

`carrying out the mode of operation described prises condensing a halogen derivative of an may condense the derivative in the vicinity of a body to be heated, it being understood, of course, that the terms "evaporation" and condensation include the separation of a gas from, and the absorption of a gas in, an absorbent respectively.

Uur invention will probably find its greatest utility by adjusting both the mode of preparing the refrigerant to obtain desirable characteristics and the mode of usingl the refrigerant to obtain a process of refrigeration or heat transfer which meets the. limitations imposed. We prefer to employ refrigerants boiling above 60 C.

Obviously our invention is not limited in its application to any specific form of apparatus for and it will not be necessary for a complete understanding pf the invention to show a specific embodiment of apparatus. Nor is the present invention limited to the` examples set forth for a particular advance of the present invention resides in the fact that a great number of new refrigerants with graduated properties is rendered available, and that one is accordingly enabled to secure the most suitable refrigerant for varied purposes.

We claimzy 1. The process of refrigeration which com- Vprises condensing a halogen derivative of an aliphatic` mono fluoride and then evaporating the said derivative in the vicinity of a body to be cooled.

2. The process of refrigeration which comalkyl mono fluoride and then evaporating the saidA derivative in the vicinity of a body to be cooled. l

3.\The process of refrigeration which comprises condensing a halogen derivative of methyl iluoride and then evaporating the said derivative in the vicinity of a body to be cooled. 4. ,The process of refrigeration which comprises condensing a iluoro-halo derivative of methane and then evaporating the said derivative in the vicinity of a body to be cooled.

5. The process of refrigeration which comprises condensing a nuoro-chloro derivative of methane ,and then evaporating the said derivative in the vicinity of a body to be cooled.

8. The process of refrigeration which comprises condensing difluoro-dichloro methane and then evaporatng it in the vicinity of a body to be cooled.

7. The process of refrigeration which comprises condensing a iluoro halo derivative of an aliphatic hydrocarbon and then evaporating the said de!- rivative in the vicinity of a body to be cooled.

8. The process which comprises substituting halogen for hydrogen in an aliphatic monofiuoride to thereby obtain a heat transfer agent having predetermined requirements of vapor pressure, toxicity, and inilammability, evaporating the heat transfer agent and condensing the evaporated agent.

9. The process which comprises substituting halogen for hydrogen in an aliphatic monoiluoride to thereby obtain a refrigerant having predetermined requirements of vapor pressure, toxicity, and inilammability, evaporating the said refrigerant and condensing the evaporated refrigerant.

10. The process of producing refrigeration which comprises condensing a nuoro-chloro derivative of an aliphatic hydrocarbon and then evaporating the said derivative in the vicinity of a body to be cooled.

11.V Ihe process of producing refrigeration 150 which comprises condensing a uoro-bromo derivative of an aliphatic hydrocarbon and then evaporating the said derivative in the vicinity of a body to be cooled.

12. The process of refrigeration which comprises condensing a bromo-fluoro derivative of methane and then evaporating the said derivative in the vicinity of a body to be cooled.

13. The process of refrigeration which comprises condensing monoluoro-dichloro methane and then evaporating it in the vicinity of a body to be cooled.

14. The process of refrigeration .which comprises condensing aA fluoro-halo derivative of ethane and then evaporating the said derivativel 18. The process of refrigeration which comprises condensing diuoro-tetrachloro ethane and then evaporating it in the. vicinity of a body to be cooled.

19. The process 'of transferring heat comprises condensing a fluorq-halo derivative of an aliphatic hydrocarbon and evaporating the said` derivative.

20. The -process of transferring heat which comprises condensing a nuoro-chloro derivative of an aliphatic hydrocarbon and evaporating the said-derivative.

V21. The process of transferring 'heat which comprises condensing a halo-nuoro derivative of methane and evaporating the' said derivative.

22. The process of transferring heat. which comprises condensing a chloro-nuoro derivative of methane and evaporating the said derivative.

23. The'process of transferring heat which comprises condensing a halo-uoro derivative of ethane and then evaporating the said derivative.

24. The process of transferring heat which comprises condensing al chloro-nuoro derivative of ethane and then evaporating the said `de- Y rivative.

THOMAS MIDGLEY, JR. ALBERT L. HENNE. ROBERT R. MCNARY. 

